1. Field of the Invention
The present invention relates generally to an automatic transmission primarily intended for motor vehicle use, and more particularly, to a method of in-gear tolerance control for a transmission that is controlled electronically and hydraulically.
2. Description of Related Art
In recent years, an advanced form of transmission control has been proposed, which offers the possibility of enabling an automatic transmission to adapt itself to changing conditions. In this regard, U.S. Pat. No. 3,956,947, issued on May 18, 1976 to Leising, et al., sets forth a fundamental development in this field. Specifically, this patent discloses an automatic transmission design which features an "adaptive" control system that includes electrically operated solenoid-actuated valves for controlling certain fluid pressures. In accordance with this electric/hydraulic control, the automatic transmission would be "responsive" to an acceleration factor for controlling the output torque of the transmission during a shift from one ratio of rotation (between the input and output shafts of the transmission) to another. Specifically, the operation of solenoid-actuated valves would cause a rotational speed versus time curve of a sensed rotational component of the transmission to substantially follow along a predetermined path during shifting.
Currently, there exists a comprehensive four-speed automatic transmission system which features fully adaptive electronic control. An example of such a transmission control system is disclosed in copending application, Ser. No. 187,772, filed Apr. 29, 1988 and entitled "AN ELECTRONICALLY-CONTROLLED, ADAPTIVE AUTOMATIC TRANSMISSION SYSTEM" by inventors Leising et al, which is commonly owned by the assignee of the present application. The transmission control system includes a microcomputer-based controller which receives input signals indicative of engine speed, turbine speed, output speed (vehicle speed), throttle angle position, brake application, predetermined hydraulic pressures, driver selected gear or operating condition (PRNODDL), engine coolant temperature, and/or ambient temperature. This controller generates command or control signals for causing the actuation of a plurality of solenoid-actuated valves which regulate the application and release of pressure to and from the frictional units of the transmission system. Accordingly, the controller will execute predetermined shift schedules stored in the memory of the controller through appropriate command signals to the solenoid-actuated valves and the feedback which is provided by various input signals.
Whenever the automatic transmission for the above control system is operating in an in-gear condition (i.e., reverse, 1st, 2nd, 3rd, or 4th gear), there is a specific known ratio that exists between the transmission's input and output shaft speeds for the given in-gear condition. Input and output speed sensors of the transmission are continuously being monitored to provide the controller with the speed data necessary to perform various control tasks. Significantly important to good shift quality with adaptive controls is the ability to rapidly identify when a friction element begins to slip during a shift. This slip is typically identified whenever the calculated input speed is different than the product of the current gear ratio times the calculated output speed by a predetermined amount called "in-gear-tolerance (IGT)". The magnitude of IGT is highly dependent on the actual physical tolerance of the teeth on the sensed speed gears, the speed sensor tooth detection circuitry, the current in-gear ratio, and actual component speeds. The effects of rough road surfaces also needs to be considered in IGT to prevent possible false identification of slip due to road generated noise. Adding an amount to IGT for rough roads, however, can result in delaying the identification of slip when operating the vehicle on a smooth road surface.
It is, therefore, one object of the present invention to provide a method of determining and controlling the in-gear tolerance.
It is another object of the present invention to provide a variable in-gear tolerance.
It is a further object of the present invention to provide an adaptive in-gear tolerance.